Gens is a free Sega Genesis emulator. It
runs on Windows systems (using DirectX), on Linux (using SDL)
and on Microsoft's Xbox. A port to the Sega Dreamcast, known as
Gens4All, is currently in development. Development of Gens began
in 1999. As of July 2006, the current version (2.14) advertises
full compatibility with 92% of all Genesis games and is
considered to be one of the most compatible Genesis emulators
available, although its Yamaha YM2612 emulation is far from
perfect[citation needed].

Retro Gamer called Gens "perhaps the best Mega Drive emulator
available".[1] VTEmulation gave Gens a rating of 10/10.[2]

Gens/GS is David Korth's fork of Gens, initially based on Gens
for Linux v2.15.5. Much like Gens, Gens/GS is a free Sega
Genesis emulator. It runs on various systems to include Windows,
Linux, Microsoft's Xbox, and Haiku.-Wikipedia